CCK, dietary variety, and food intake in rats /

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Abstract

Among the environmental factors that can affect food intake is the extent of dietary variety
available in the environment. Numerous studies have demonstrated that variety in a meal can
increase the amount of food consumed in humans, rats, and other species. A physiological
mechanism that has been demonstrated to affect food intake is the gut peptide cholecystokinin
(CCK) which is released from the upper small intestine during the ingestion of food. Peripherally
administered CCK has a robust inhibitory effect on the intake of a single-food meal. Thus, dietary
variety and CCK both affect meal size, with dietary variety increasing intake and CCK decreasing
intake. This raises the question ofhow dietary variety and CCK might interact to affect meal size.
Previous studies of CCK's effects have focused on situations in which only one food was available
for consumption. However, in an animal's natural environment it would frequently occur that the
animal would come across a number of foods either simultaneously or in quick succession, thus
providing the animal access to a variety of foods during a meal. Accordingly, the effect ofCCK
on food intake in single-food and multiple-food meals was examined. It was found that food
intake was greater in multiple-food than in single-food meals provided that foods in the multiplefood
meal were presented either simultaneously or in increasing order of preference. When foods
in the multiple-food meal were presented in decreasing order of preference, intake was similar to
that observed in single-food meals. In addition, it was found that CCK inhibited food intake in a
dose-dependent manner, and that its effects on food intake were similar regardless of meal type.
Therefore, the inhibitory effects ofCCK were not diminished when a variety of foods were
available for consumption. Furthermore, the finding that CCK did not differentially affect the
intake of the two types of meals does not provide support for the recent-foods hypothesis which
postulates that CCK decreases food intake by reducing the palatability of only recently consumed
foods. However, it is consistent with the all-foods hypothesis, which predicts that CCK reduces
food intake by decreasing the palatability of all foods.
The 600 ng/kg dose of the CCK^-antagonist lorglumide significantly antagonized the
inhibitory effect of exogenous CCK on food intake, and the magnitude of this effect was similar
for both types of meal. These results suggest that exogenous CCK inhibits food intake through
the activation ofCCK^ receptors. However, when administered by itself, the 600^ig/kg dose of
lorglumide did not increase food intake in either single-food or multiple-food meals, suggesting
that peripheral endogenous CCK may not play a major role in the control of food intake.